The activity of PCP (phencyclidine) is discussed in NIDA Notes 2 (1987) 9. This article sets out the binding of PCP to two different receptors of the nerve membranes. MK-801, (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]-cyclohepten-5,10-imine maleate is known as potent anticonvulsant, and it is also known that MK-801 is a potent N-methyl-D-aspartate (NMDA) antagonist: Proc. Nat. Acad. Sci. U.S.A. 83 (1986) 7104. The kinetic characterization of the phencyclidine-NMDA receptor interaction, setting out evidence of a steric blockage of the channel was described in Biochem. 27 (1988) 843. It is known that there exist a number of excitatory amino acid antagonists, some of which block the neurotoxic activity of N-methyl-aspartate (NMDA). Amongst the most effective of these are phencyclidine (PCP) and MK-801, see Europ. J. Pharmac. 141 (1987) 357.